The present invention relates to a method of measuring atmospheric pressure, and particularly relates to a method of measuring atmospheric pressure necessary for computing a fuel quantity in an internal conbustion engine by use of measurement of negative pressure in a suction pipe.
FIG. 1 is a diagram illustrating a basic arrangement of a suction system of an engine, and is also utilized for explanation of the atmospheric pressure measuring method according to the present invention which will be described later.
In FIG. 1, a suction pipe 2 is connected to an air cleaner 1 for eliminating dust in the air.
The suction pipe 2 is provided with an injector 3 and a throttle valve 4. The injector 3 is controlled by a computer described later so as to inject gasoline fuel. The throttle valve 4 is manually operated by an operator. The opening of the throttle valve 4 is converted into a voltage signal by a throttle opening sensor 5 to be outputted therefrom.
A boost sensor 6 is arranged to detect the pressure (mainly negative pressure) in the downstream of the throttle valve 4 of the suction pipe 2. The temperature of suction air in the suction pipe 2 is measured by a suction temperature sensor 7. On the other hand, the temperature of cooling water for an engine 10 is detected by an engine water temperature sensor 8.
An intake-manifold 9 distributes a mixture of air from the air cleaner 1 and gasoline injected from the injector 3 to the engine 10.
An exhaust gas burnt in the engine 10 flows out through an exhaust-manifold 11.
A computer 12 receives signals from the throttle opening degree sensor 5, the boost sensor 6, the suction temperature sensor 7, and the engine water temperature sensor 8 and signals from a not-shown ignition system so that the computer 12 computes the rotational speed of the engine and provides instructions to the injector 3, etc. on the basis the received signals. An atmospheric pressure sensor 13 supplies atmospheric pressure information to the computer 12.
Next, the operation of the system will be briefly described. The respective outputs of various sensors including the throttle opening degree sensor 5, the boost sensor 6, the suction temperature sensor 7, the engine water temperature sensor 8, the atmospheric pressure sensor 13, and O.sub.2 sensor (not shown), an EGR opening degree sensor (not-shown), an engine rotational speed detector (not shown), and so on, are inputted to the computer 12 so as to evaluate the operating condition of the engine.
The computer 12 determines, from the signals of the various sensors, a predetermined optimum quantity of fuel injection so as to send an electric signal to the injector 3, and at the time sends signals to other actuators to control them so that the exhaust gas, fuel efficiency, driving feeling, and so on, of the car are made to be always optimum.
In the method of measuring atmospheric pressure in the conventional system, there have been problems in that the atmospheric pressure sensor 13 which has the same structure as the boost sensor 6 is separately provided to measure atmospheric pressure, that is, two sensors of the same kind are required to be provided, so that the system is expensive and an excessive space is required. Moreover, there are variations in characteristics between the two sensors so that the accuracy of the measurement is deteriorated.
As disclosed in a prior art reference (Japanese Patent Unexamined Publication No. 61-205832), there has been proposed a method in which a single boost sensor 6 is used and the boost pressure output is operated to calculate atmospheric pressure. This method, however, has a problem that the frequency of detection of atmospheric pressure is low because an average value of the output of the boost sensor is considered.